Method for obtaining plutonium metal and alloys of plutonium from plutonium trichloride



N0V- 13, 1962 J G REAvls ET'AL 3,063,829

METHOD FOR OBTAI'NIN'G PLUTONIUM METAL AND ALLOYS 0F PLUTONIUM FROMPLUTONIUM TRICHLORIDE 5 Sheets-Sheet 1 Filed April 8, 1960 7'0 VacuumAnd Argan INVENTOR MTM-S555. James G. Real/s, Joseph A. Leary,

V/ M di, MII/gn J. Maraman j 1f cn. .B ma. M WM United States PatentOffice 3,063,829 Patented Nov. 13, 196,2

METHQD FOR OBTAINIG PLUTONIUM METAL AND ALLQYS F PLUTONIUM FRGM PLUTO-NIUM TRICHLORIDE James G. Reavis, Joseph A. Leary, and William J.Maraman, Los Alamos, N. Mex., assignors to the United States of Americaas represented by the United States Atomic Energy Commission Filed Apr.8, 1960, Ser. No. 21,073 5 Claims. (Cl. 75-84.1)

The present invention relates to methods for obtaining plutonium metaland plutonium alloys by the direct reduction of plutonium halides, andis more particularly concerned with such methods wherein a reducingmetal which forms a chloride having a more negative standard free energyof formation than that of plutonium trichloride is used to reduce suchplutonium trichloride. It is also within the scope of the presentinvention to perform such reductions with a reducing metal which doesnot appreciably reduce certain contaminating halides which may bepresent.

The present application is an undiminished continuation-in-part ofapplication Serial No. 820,836, tiled .Tune 16, 1959, entitled MethodFor Obtaining Plutonium Metal From Its Trichloride. 'the new materialadded hereinbelow is that relating to cerium reductions of PuCl3 toobtain plutonium-cerium alloys and, when cobalt is added, toobtain`PuCe-Co ternary alloys. The properties of such alloys which makethem useful as reactor fuels are disclosed in the patents issued toCothnberry, U.S. Pat. 2,867,530 and 2,901,345.

The standard prior art method for obtaining plutonium by a reduction ofits halides consists in the calcium reduction of plutonium tetraiiuoridein the presence of iodine, U.S. Pat. 2,890,110. Advantage is taken ofthe exothermic reaction between iodine and calcium to limit the heatrequired from external heat sources to that required to initiate thecalcium reduction of the luoride, the reactions thereafter beingself-sustaining, and an excess of calcium ovei that required for boththe reduction of the PuF4 and the iodide formation is used to push thereactions in the desired direction and thereby increase the yield. Theexotherrnic heat of both reactions is also useful in keeping theplutonium and the slag in a molten condition for their ready separation.

The Baker process has come to be known as the bomb process because thereactions are necessarily conducted inside a heavy sealed metalcontainer. The container must be evacuated, filled with argon and sealedafter charging at room temperature to prevent oxidation of thereactants. The argon also reduces the extent to which the iodinepenetrates the pores of the refractory liner inside the metal container.The container must have a heavy wall because high internal pressures aredeveloped during the process, even before the other reactants combinewith iodine. At 260 C., for example, probably all the iodine has beenvolatilized to create a partial pressure of about 6 atmospheres. As thetemperature inside the container increases, further pressure increasesare brought about by simple heating of both the iodine vapor and theargon. The free volume inside the container must be kept to a minimum toconfine the iodine to the reaction zone, and thus the high pressurescannot be avoided by increasing the Volume of the container.

Thus the only practicable bomb process is that in which the solid dryreactants are charged into the bomb at room temperature with a smallfree volume in the space above the charge. The bomb is sealed with agasketed and bolted cover plate, the air in the free volume is replacedwith argon, and the charge is heated by an atmosphere.

induction coil. After a few minutes, the temperature inside the reactionvessel begins to rise rapidly, induction heating is discontinued and thereaction is allowed to proceed at its own pace. After a rapid rise to amaximum temperature somewhere in the range of 1000 to 1600 C., thecontents of the vessel are allowed to cool to room temperature. The-bomb is opened to yield a solid plutonium button at the bottom and asolidified CaF2CaI2 slag at the top.

The principal disadvantages of the bomb process as outlined above arethat (l) it requires the use of iodine and extra calcium; (2) it isessentially a high pressure process and requires a thick-Walled reactionvessel and (3) it is not amenable to continuous or semi-continuousoperation, but is strictly a batch type operation. It is an object ofthe present invention to provide a process for obtaining plutonium metalthrough the reduction of plutonium halides which does not have suchdisadvantages.

Another object of the present invention is to provide methods and meansfor obtaining pure plutonium metal in high yield by reduction of thehalides of plutonium without the use of booster reactants to provide aconcurrent heat liberating reaction.

A further object is to provide such methods and means for obtainingplutonium metal wherein the pressure in the reaction vessel is neverappreciably greater than that of the surrounding atmosphere.

An additional object is to provide such methods and means in which thereaction will contain the resulting reaction products in the moltensolid states but has walls of a thickness not necessarily greater thanthat required for reactions at atmospheric pressure.

Another and further object is to provide such methods and means in whichthe products may be withdrawn continuously or semi-continuously, i.e.,complete shutdown is not required except momentarily and/or after a longperiod of operation.

An additional object is to provide such methods and means whereinsubstantially pure plutonium metal is obtained from a plutonium halidecontaminated with like halides of ssion product elements, the bulk ofthe latter halides appearing in the slag.

Yet another object is to provide a process for both reducing theplutonium in a molten halide thereof to the metallic state andsimultaneously alloying such plutonium with a reductant or with bothsuch reductant and a third metal, which does not enter into thereaction, both types of alloys being useful as reactor fuels.

Still another object is to provide a method such as the foregoing whichdoes not require the use of booster reactants, wherein the pressure inthe reaction vessel is never appreciably greater than atmospheric anddoes not require a thick walled vessel, and the plutonium is separatedduring the process from ssion products, the bulk of such contaminantsappearing in the slag rather than the alloy.

The above and other objects are attained in the present invention by thedirect reduction of plutonium trichloride (PuCl3) with any one ofseveral metals in a heated container filled with an inert gas, which maybe initially at a pressure somewhat less than atmospheric but in noinstance need be more than approximately atmospheric. The salt is meltedunder such pressure, after which the inert gas pressure is increased, ifnecessary, to about an The reductant is then added gradually, and thetemperature is increased while maintaining the inert gas pressure atabout an atmosphere. In the case of forming the Pu-Ce-Co alloys, theCe-Co alloys are added in the form of sizeable chunks, eg., of l/z-in.dimensions, at the outset, and are allowed to react with the saltthroughout all of the heating. This is the only practicable method ofadding the reductant alloys used, as they have `with the explosiveviolence of calcium, and there is no need for extreme caution incombining the reactants.

A non-reacting halide such as NaCl may be added with the PuCl3 to serveas a flux, i.e., to reduce the melting point of the resulting salt slagbelow its undiluted value of 772 C. (CaCl2) or 870 C. (LaCl3) or 810 C.(CeCl3). An alternate method of avoiding high pressures withoutvolatilization or air leakage into the reaction vessel is to maintainthe inert gas at a pressure slightly greater than that of thesurrounding atmosphere and to allow gas to leak from the vessel at arate sufficient to prevent any appreciable increase in pressure. Thismethod was used in the cerium and cerium-cobalt reductions to bedescribed below.

The method of the present invention can be more easily understood byreferring to the attached drawings, of which:

FIGURE l illustrates apparatus suitable for conducting the processes ofthe present invention in a batchwise fashion, and was used with slightmodifications in the work summarized in the examples below,

FIGURE 2 shows an 'apparatusl suitablefor carrying on the same processessemi-continously, and

FIGURE 3 depicts apparatus inhwhich. some of the same processes may becarried on continuously.

Turning now to FIGURE l, the general procedure is to charge the chlorideor chlorides v1 in powder form into a suitable crucible 2. The crucible2 is :placed inside a furnace tube 3, which may be of a wall, thicknessno greater than that needed to withstand a vacuum and may, eg., be ofquartz for ready observation. The furnace tube 3 is sealed with astopper 4 fitted with avthermocouple well 5, a tube 6 for connection toa vacuum pump and an argon supply system, and a tube 7 for the additionof calcium or other granular reductant, the thermocouple well andreductant tube 7 extending down into the crucible. The reductant tubemay be conveniently terminated on the outside in a ground glass joint Sslanted from the vertical as shown, the other member of such joint beingconnected to an otherwise closed container 9 lled with granularreductant 10 and having the bent section indicated. By pivotingcontainer 9 about joint 8, reductant 10 may be added at the will of theoperator without affecting the atmosphere Within the furnace tube. Thecrucible 2 is fitted with a tantalum lid 11 having appropriate openingsfor the reductant tube 7 and thermocouple well 5, and a number ofsmaller vapor openings as well. The purpose of lid 11 is to reducelosses of reactants and products from crucible 2 by spattering andvolatilization. j

With all of the above components installed as indicated, the furnacetube is evacuated of air, and heat is supplied to raise the temperatureVof the crucible contents rather slowly while evacuation is continued.This is done to remove moisture and occluded gases from the reactantsand the reaction vessel. When such temperature is between 200 C. and 450C., argon is admitted to a pressure of about half an atmosphere toprevent volatilization or spattering of the salt in the crucible. Thispressure is somewhat arbitrary and was selected to insure a tightconnection at ground glass joint 8 (with atmospheric pressure outside)and also to insure against a too rapid increase in pressure within thereaction vessel during heating. With gas tight seals at all openings anda relief valve in gas line 6, such precautions are unnecessary, and apressure of about an atmosphere may be used throughout i all heating.This was the technique used in the cerium and cerium-cobalt reductionsdescribed below. In using the FIGURE l embodiment as shown, when thedesired reduction temperature is reached, as indicated in more detailbelow, and before any reductant is added, the argon pressure is adjustedto a few centimeters of mercury 4below atmospheric. This pressureincrease reduces the stress on the tube 3 by the atmospheric pressure onthe outside, insures against air leakage into the tube, and preventsfurther spattering in the crucible as local high temperatures or hotspots may develop in the reactants and products.

In some cases, specifically, the lanthanum and cerium reductionsdescribed below, the apparatus pictured in FIG. l was modified to permitintroduction of the reductant as a solid rod. This is desirable becauseit permits the use of pyrophoric and easily oxidizable material in amore convenient form, and also because it permits withdrawal of theunused portion of the reductant ro-d when the reduction is completed, atleast for those reductants which do not alloy with plutonium. As notedbelow in connection with Example ll, it is not particularly desirablefor the second purpose with ceriumfas the excess rod absorbs plutonium.The reductant introduction tube was replaced by a molybdenum rod ofsmall diameter which was used to suspend the rod of reductant. Thetemperature and pressure of the system were ad justed as outlined inpreceding paragraphs before addition of the reductant. The bar ofreductant was then lowered by pushing down the molybdenum rod to immersethe end of the reductant bar in the PuClg-containing salt. As the end ofthe bar was used up in the reaction, the bar was lowered further to addmore reductant to the system. After an appropriate reaction time thereductant was withdrawn from the salt, in the case of lanthanum, and thesystem was cooled. The cerium reductions demonstrated that thewithdrawal of excess cerium is impractical.

The apparatus of FIGURE l defines a large gas volume above the reactioncrucible, this volume extending, in the particular apparatus used, aboutll inches above the 4-inch high crucible in the 2-inch LD. furnace tube.The large volume of gas acts as a cushion for the expan- V sion oflocally heated gas, i.e., the gas contacting the reactants and products.When the apparatus was used in the reductions of the examples below, nosignificant pressure increase occurred after the adjustment describedabove, i.e., the total pressure remained at about atmospheric during thereductant addition and thereafter. This large gas volume also served thepractical purpose of insulating stopper 4 from the high temperature ofthe reaction zone. With a refractory type closure and the appropriaterelief valve mentioned above, such volume can be reduced considerably.

Using the above described apparatus and generally described method, twoattempts were made to reduce PuCl3 in a PuClS-NaCl mixture by gradualaddition of small pieces of Mg to the Vmolten salt mixture in a quartzcrucible. In both cases the yield of Pu metal was too low to beacceptable (less than A number of calcium reductions were made using'both pure PuCl3 and PuCl3-NaCl mixtures, and using each type of salt inboth tantalum crucibles and in ceramic crucibles composed of l0 percentby weight (w/o) of TiO2, balance MgO. In each case, 25 percent molarexcess of granular Ca was used as the reductant. Also in each case, theplutonium chloride was prepared from plutonium metal of about 99.9percent purity. Four reductions of PuCl3 from PuClB-NaClrmixtures weremade by dipping lanthanum rods into the molten salt contained in MgO- 10w/o TiO2 crucibles, the total amount of La present in each reductionbeing in large excess of the amount needed for complete reduction of thePuCl3. After the reaction had proceeded for the desired length of time,the excess La was withdrawn to break contact with the salt.

A number of reductions of PuCl3 were accomplished by dipping cerium rodsinto molten salt contained in MgO-lO w/o Ti02 crucibles, the amounts ofthe reactants varying as indicated in the specific examples below. Thequartz furnace tube was evacuated after introduction of the reactantsand while heating to above 100 C. but not above 450 C., after which thetube was filled to `and maintained at atmospheric pressure with argonduring the balance of the run. Conditions were the same for thecerium-cobalt reductions exemplified below except that the Ce-Co wasadded to the salt at the outset as massive pieces, as already noted.After completion of the heating cycle in each run, the cooled cruciblewas broken to yield a well formed massive metal lbutton well separatedfrom the solidified halide slag. The buttons were cleaned and analyzedfor Pu, Ce, La and Co, as noted in each case.

Specic examples of the above methods and results follows:

(l) Ca Reduction, Tantulum Crucible, Undiluted PruCla After reaching asteady temperature of 773 C. as indicated by a thermocouple junction atthe bottom of the well, the calcium was added at the rate of 0.5 to 1.0gram per minute. The maximum temperature observed during the Ca additionwas 850 C. because of the exothermic nature of the reaction. At the endof such addition, the temperature of the reaction products was 803 C.Heating was discontinued and the contents of the crucible were allowedto co-ol to room temperature. The bulk of the slag was removedmechanically, and the vbalance by leaching with dilute HNO3.

The plutonium metal in the crucible presented a smooth, dense surface,and was removed by dissolution in dilute HC1. The metal contained about0.1 weight percent Ca, 0.02 weight percent Ta, and the balanceessentially plutonium (98.5 w/o). The yield from a starting weight ofplutonium in the chloride of 25.02 grams was 99.9 percent. The slagcontained 0.06 weight percent PuCl3 and accounted for 0.03 percent ofthe starting weight of plutonium.

(2) Ca Reduction, MgO-TiOZ Crucible, Undiluted PuCl3 The rst calcium wasaddedto a quantity of fused PuCl3 containing 16.65 grams of plutonium inthe crucible after the argon pressure had been adjusted to a fewcentimeters less than atmospheric at a steady temperature of 757 C. Thecalcium addition was continued at the rate of 0.5-1.0 gram per minuteuntil the 25 percent molar excess had been added, during which time thetemperature in the crucible rose to 785 C. Since previous reductions hadindicated the necessity for la further increase in temperaturc to obtaina smooth, mechanically separable Pu regulus when using the oxidecrucible, the yfurnace heating rate was increased to raise the crucibletemperature to 850 C. At this point the furnace was shut off, and thetube and contents were all-owed to cool to room temperature.

The ceramic crucible was broken open, and the metal butt-on andsolidified slag were mechanically separated. The plutonium was leachedwith dilute HNO3 to remove adhering siag and calcium, after which it wasdried, weighed, and dissolved in dilute HC1 for analysis. The separatedslag was similarly weighed and dissolved in dilute HNOS for analysis.

The results of the analyses indicated a 95 percent plutonium yield, with4 weight percent of the slag consisting of PuCl3 and accounting for 2percent of the starting plutonium the balance presumably appearing inthe crucible). The plutonium button was found to contain less than 0.03weight percent Ca, the balance being essentially all Pu, i.e. Pu 99.0Weight percent.

(3) Ca Reduction, Ceramic Crucible, 80 w/o PuC13-20 w/o NaCl Sull Themixed salts contained 9.35 grams of plutonium. Calcium addition wascommenced at 575 C. and continued through a crucible temperature rise to590 C. at

the rate of 0.5-1.0 gram per minute. The heating rate was increaseduntil the crucible temperature rose to 850 C., after which the furnacewas shut off and the tube and contents were cooled to room temperature.

The products were separated for analysis as in Example 2, again yieldinga dense plutonium button. The analyses indicated a plutonium yield of98.5 percent, with the slag consisting of 0.07 weight percent Puclg andaccounting for 0.5 percent of the starting plutonium. The metal buttoncontained 0.02 weight percent Mg, 0.01 weight percent Ca, 0.10 weightpercent Ti, balance essentially pure plutonium 99.0 weight percent).

(4) Ca Reduction, Ta Crucible, 80 w/o PuCl3-20 w/o NaCl Salt The mixedsalts contained 13.43 grams of plutonium. Calcium was added at the rateof 0.5-1.0 gram per minute in the range of 700-715" C. It was found thata dense pool of molten plutonium forms at 715 C. and that heating to ahigher temperature is unnecessary. The furnace was shut down at 715 C.and the products cooled to room temperature.

The crucible contents were removed as in Example 1, disclosing a smooth,dense plutonium button. The metal and slag were weighed and analyzed toindicate a plutonium yield of 98.5 weight percent, with 0.05 percent ofthe starting plutonium appearing in the slag. The metal contained about0.10 weight percent Ca and 0.02 weight percent Ta, balance essentiallypure plutonium 99.0

weight percent). (5) Ca Reduction, Ceramic Crucible-Coiztaminaled SaltThe same type of MgO-lO weight percent TiOZ crucible as in Example 3 wasused, but the salt mixture contained 5 weight percent mixed rare earthchlorides, 19 Weight percent NaCl and 76 weight percent PuCl3. Followingthe same procedure of adding calcium slowly when the argon pressure isslightly less than atmospheric, the addition was started at 520 C. andcontinued to 565 C. The crucible temperature was raised to 860 C., afterwhich the furnace was shut down and the tube allowed to cool to roomtemperature.

Upon separating and analyzing the products in the usual manner, it wasfound that the plutonium yield was 99 percent, the PuCl3 concentrationin the slag being 0.4 weight percent `and accounting for 0.45 percent ofthe starting plutonium. However, the plutonium button analysis revealedthat virtually all of the rare chlorides had been co-reduced with thePuCl3, and accounted for an appreciable fraction of the weight of thebutton.

The work summarized in the above examples was also repeated withdecreasing molar excesses of calcium. This further work indicated that al5 percent molar excess of calcium is required to insure a plutoniumyield exceeding percent, and that at least a 20 percent calcium excessis necessary to obtain the high plutonium yields of the examples, i.e.,to 99.9 percent.

(6) La Reduction, Ceramic Crucible, PuClS-NaCl Salt The lanthanumreductant Was added to a fused salt melt consisting of 79 weight percentPuCl3 and 21 weight percent NaCl after the latter had been raised to atemperature of 700 C. and the argon pressure above the crucible hadreached atmospheric pressure. The lanthanum was in the form of a rod of0.5 cm.2 cross sectional area, the addition being accomplished bylowering the La rod into the melt from a 1z-inch diameter molybdenumsuspension rod passing through the stopper of the furnace tube. As theend of the La rod was consumed during the reaction, the balance of therod was lowered to add fresh reductant to the melt. The amount of Lathus contacted was in large excess of the stoichiometric amount for thecomplete reduction of the PuCl3.

After 25 minutes at 700 C., during which not more than 10 C. risebecause of exothermic reaction was observed, the La'rod was withdrawnand heating was discontinued. The cooled crucible was broken open toreveal a well formed plutonium button. Upon separation of the metal fromthe slag and subsequent analysis, it appeared that the yield of Pu was91.percent from a starting weight of 13.64 grams in the trichloride. Theconcentration of La in the metal was less than 0.007 weight percent, andthe concentration of PuCl3 in the slag was 7.0 Weight percent.

(7) La Reduction, Ceramic Crucible, PuClg-NaCl Salt Example 6 wasrepeated, the only difference being that the composition of the saltphase was 80 weight percent PuCl3-20 weight percent NaCl, the Weight ofthe combined Pu being 20.07 grams.

"1n this instance the yield of plutonium in a well formed button was 90percent, the concentration of the lanthanum -therein being 01.27 weightpercent. The concentration of the PuCl3 in the slag was 6.0 weightpercent.

La Reduction, Ceramic Crucible,

PuCla-NaCl-CeCla Salt (9) La Redaction, Ceramic Crucible,

PuCl3-NaC1-CeCl3 Salt Example 8 was repeated with a salt melt ofcomposition 78 weight percent PuCl3-l9.7 Weight percent NaCl-2.3 weightpercent CeCl3 containing 17.37 grams Pu and 0.41 gram Ce in thechlorides. The Pu yield was 95 percent, and the metal was found tocontain 0.17 weight percent La and 0.09 weight percent Ce. Theconcentration of PuC13 in the slag was 1.4 weight percent.

(10) Ce Reduction and Pu-Ce Alloy Formation A cerium rod, approximatelythree inches long and Weighing about 13 grams, was slowly added to24.137 grams of a salt melt consisting of about 78 W/ o PuCl3, 19.5 W/oNaCl and 2.5 w/o LaCl3 blanketed by argon at prevailing atmosphericpressure. The addition was rnade over a 20 minute period While thetemperature was held in the range 688-698 C. This temperature was heldfor an additional 10 minutes and the system was then cooled. Analysis ofthe metal button which was produced showed that 93% of the startingweight of the plutonium appeared in the alloy, which consisted of 73 w/oPu, 27 w/o Ce and less than 0.06 W/o La. The La/Pu weight ratio hadchanged from 0.029 in the original salt to less than 0.0008 in theproduct alloy, giving a lanthanum decontamination factor greater than35, i.e., theV ratio of lanthanum to plutonium in the original saltdivided by the ratio of lanthanum to plutonium in the product wasgreater than 35.

(11) A cerium rod Weighing 18.49 grams was slowly Y added to 34.863grams of molten 76.2 w/o PuCl3, 19.7 w/o NaCl, 4.1 w/o LaCl3 over a 20minute period at 660-685 C. A small fraction of the cerium bar wasretrieved at the end of this period -while the salt and alloy remainingVthe Crucible were maintained in this temperature range an additional 10minutes before cooling. The metal button was found to contain 91% of thetotal plutonium in the system as an alloy of 84 W/o Pu, 16 w/o Ce and0.07 w/o La, indicating a lanthanum decontamination factor of 50. Thecerium bar which had been withdrawn contained 7.0% of the totalplutonium in the system in an alloy consisting of 35 w/o Pu and 65 w/oCe. The alloy formed in the cerium rod appeared to be s homogeneous, theplutonium having migrated above the level of the molten salts. Whilethis might prove to be a useful technique for forming Pu-Ce alloys ofhigh cerium content, it is not considered particularly desirable to formtwo Pu-Ce alloys of different compositions in the process of the.present invention. This example indicates the necessity for determiningthe amount of cerium in ad- Vance of operation, and actually adding allof the cerium thus determined.

(12) A cerium rod weighing 13.265 grams was added to 35.447 grams of thesame salt mixture as was used in Example 11. The addition Was made overa 10 minute period at a temperature of 650-656" C. and the system wascooled immediately. The metal button contained 88% of the totalplutonium in an alloy of 86 w/o Pu, 14 w/o Ce and 0.03 -w/o La. Thiscomposition indicates a lanthanum decontamination factor of about 116.

(13) A cerium rod weighing 9.225 grams was added to 30.154 grams offused salt consisting of 75.3 w/o PuCl3, 19.3 w/o NaCl, 2.7 w/o CeC13and 2.7 W/o LaCl3 over a period of 5 minutes at 6934703 C. After the rodhad all been added the reduction products were held at this temperaturefor an additional 10 minutes before cooling. Analysis of the metalbutton showed 90% of the total plutonium was present in an alloy of 98.9w/o Pu, 1.1 W/ o Ce and less than 0.004 w/o La. The indicated lanthanumdecontamination factor was greater than 750. In this case the ceriumadded to the salt was 100.3% of the stoichiometric amount for a completereduction, and the results indicate the minimum cerium content of theplutonium alloy formed by such reductions to be 1.1 W/o (1.86 a/o).

(14) 10.109 grams of cerium was added to 31.180 grams of fused saltcontaining 75.2 w/o PuCl3, 19.9 w/o NaCl, 2.2 W/ o CeClS and 2.7 w/oLaCl3 over a 10 minute period at a temperature of 690710 C. Thereduction products were immediately cooled at a rate of 2 C./ min.

` The metal button contained 90% of the total plutonium in an alloy of97.4 w/o Pu, 2.6 W/o and less than 0.1 w/o La. The lanthanumdecontamination factor was greater than 24.

Ce Redaction and Pu-Ce-Co Alloy Formation In Examples 15-18 below, thereductant alloy was 5.5 w/o Co, 94.5 w/o Ce (12 a/o Co, 88 a/o Ce), andthe salt composition was 75.2 W/ o PuCl3, 19.9 w/o NaCl, 2.2 w/o CeCl-,and 2.7 w/o LaCl3, the latter being used as a representative rare earthssion product contaminant. CeCl3 was included in the salt simply becauseit was available from Vprevious reductions with lanthanum; it is inerthere and could have been omitted without effect. The chunks of metalwere combined with the salt at room temperature, heated slowly to about100 C. while evacuating, then more rapidly to the reduction temperatureunder streaming argon'.

(15) 18.780 grams of Ce-Co alloy were combined with 13.140 grams of thesalt and heated from about 100 C. to 775 C. at a rate of about 8 C./min.After holding at 775 C. for 4 minutes the system was cooled at about 8C./ min. Analysis of the metal button showed a plutonium yield of 98.4%in an alloy of about 32 W/ o Pu, 64 w/o Ce, 5 w/o Co and less than 0.2W/o La. (Button composition percentages do not add up to 100% because ofanalytical errors.) This corresponds approximately to an alloy of 20 a/oPu, 12 a/o Co and 68 a/o Ce, which was the desired product. In theprocess the La/Pu weight ratio changed from 0.024 to less than 0.005which indicates a lanthanum decontamination factor greater than 5. Theactual lanthanum decontamination factor may have been much greater thanthis value since the analysis set only an upper limit on the possiblelanthanum concentration in the ternary alloy. (Analyses for lanthanum insolutions of high cerium content are severely limited.)

9 with 12.033 grams of the salt and the mixture was heated at a rate ofabout l deg/min. from 100 C. to 550 C. The system was held at about 550C. for 40 minutes and cooled at about 6 deg/min. The ternary alloyproduced contained about 97% of the plutonium in the system. Thecomposition of the alloy was about 31.5 w/o Pu, 63.4 w/o Ce, 4.9 w/o Coand less than 0.2 w/o La. 'Ihe indicated lanthanum decontaminationfactor is greater' than 4.

(17) 18.411 grams of the Ce-Co alloy were combined with 12.568 grams ofthe salt and heated from about 100 C. to 635 C. at a rate of about 10deg/min. The system was held in` the temperature range 635650 C. for 12minutes and cooled at about 8 deg/min. The button contained about 93% ofthe plutonium and the composition was 31.4 w/o Pu, 64.1 w/o Ce, 5.1 w/oCo and less than 0.2 w/o La. The indicated lanthanum decontaminationfactor is greater than 4.

(18) 17.470 grams of Ce-Co alloy were combined with 31.058 grams of`salt and heated from about 100 C. to 700 C. at a rate 0f about 15deg/min. The system was held in the temperature range of 70D-720 C. for15 `minutes and cooled at about 8 deg/min. About 93% of the totalplutonium appeared in the button, which contained 66.6 w/o Pu, 29.9 w/oCe, 4.3 w/o Co and less than 0.1 w/o La. The indicated lanthanumdecontamination factor is greater than 12. The composition of this alloywas 49.3 a/o Pu, 37.8 a/o Cc and 12.9 a/o Co, which approximates theintended composition.

FIGURE 2 illustrates an apparatus suitable for practicing the presentinvention on a semi-continuous basis. This apparatus consistsessentially of a number of tubes, preferably of tantalum or othernon-reactive metal, disposed in registering and sealing relationshipwith a number of cylindrical cavities in a block 21 of non-reactivemetal which does not alloy with plutonium, e.g., tantalum, the latterbeing disposed in a furnace or being provided with heaters inserted inappropriate cavities (not shown). Thus the reaction chamber 22 registersin sealing relationship with the tube 23, the latter extending aboveblock 21 to provide a gas volume as in FIGURE 1 and tted at the top witha closure (not shown) provided with appropriate passages for saltaddition tube 24, metal addition tube 25, stirrer shaft 26 and anyauxiliary devices used, e.g., a thermocouple Well.

Through passage 27 in block 21 registers with plutonium outlet tube 28at the bottom of the block and the inert gas inlet tube 29 at the top,the latter tube being connected to furnace tube 23 by one or more crosstubes 30. Reaction chamber 22 is tapered at its lower end 31 as shownand is connected through the small Vertical cavity 32 and the diagonalriser cavity 33 to through cavity 27, this arrangement being generallyknown as an overflow Weir. By this arrangement liquid plutonium 34 candrain through the lower end of cavity 28 and out through tube 28, butthe inert gas pressure at the maximum plutonium level 36 is always equalto that at the top of the melt 37, thereby preventing a siphoning actionwhich could remove all of the liquid plutonium 34 and the melt 35 if nosuch arrangement were provided.

The stopper rod 39 operates slidably and sealingly in cavity 38 to blockany possible ow from reaction chamber 22 through cavity 40 to thesmaller bore salt drainage cavity 41 and salt drainage tube 42, asshown. Stirrer 43 is provided to agitate the melt and insure rapidcontact between the PuCl3 and the calcium, lanthanum or other metalreactant. This is highly desirable because freshly added reactants donot immediately form a uniform dispersion throughout the reaction zone.Calcium, for instance, will float on the surface 37 of melt 35, whilefreshly added PuCl3 granules tend to sink in a melt of CaCl2 or LaCl3and NaCl. Although the liquid forms of these salts, including any NaCl,are completely miscible at the operating temperature and eventually willform uniform solutions in which the PuCl3 will be reduced to form Pu andCaClz or LaCl3, the reduction I0 will be considerably hastened by theagitating action of stirrer 43.

In a starting up operation, stopper rod 39 is placed in the closedposition shown, the system is purged, and an inert gas such as argon orhelium is admitted from the top of tube 29. It is preferable to maintainthe inert gas pressure within the device at a slightly higher pressurethan that on the outside, to insure against air or oxygen leaks into theapparatus. This is most easily accomplished by pumping puriiied argon inthrough tube 29 and permitting it to leak out through plutonium exittube 2S and either or both the salt addition tube 24 and the reductantaddition tube 25. The eiuent gas may, of course, be collected andre-purified. Such a system may be made continuous by old and Well knownmethods. The iiowing gas contributes the further advantage of carryingoff some of the exothermic heat and makes it possible to reduce thelarge gas volume mentioned above.

PuCl3 (and NaCl) may then be added in powder form through tube 24,followed by heating and then gradual additions of calcium through tube25, or the apparatus may first be heated to the reaction temperature andthe salts and the reductant may be gradually added, simultaneously orseparately. These additions may be accomplished through means not shownsimilar tothe reductaut addition tube 9 of FIGURE 1, the latter beingmodied to provide a passage for the exit of the argon.

Some amount of care must be exercised in determining the weight andvolume of the initial charge to prevent the escape of unreacted PuCl3through tube 28, e.g., if only the salts are melted iirst, the chargemust be calculated to keep the liquid level in the reaction chamber 22no higher than the maximum plutonium level 36. When the initial chargehas reacted and the dense liquid plutonium has collected in the diagonalriser 33 and vertical cavity 32, the plutonium level in 33 will fallbelow the level of the fused salts in reaction chamber 22, thedifference in height depending on the relative densities of the twoliquid phases in a well known and calculable manner.

Thereafter more of the reactant salt, with or without the NaCl diluent,and more of the metal reductant may be added. Either the salts may beadded batchwise, followed by gradual additions of the metal, or both maybe added gradually at about the same time. The latter is preferredbecause it brings the reactants into contact with one another morequickly than the batchwise additions. The stirrer 43 is activated tofurther promote a rapid reduction.

from diagonal riser 33 into cavity 27, through which it falls intooutlet tube 28. As more raw materials are added and the reactioncontinues, the overow and collection of such plutonium continues. Sincethe salt continues to accumulate as plutonium is being removed, levelsafe plutonium accumulation consonant with non-criticality, the maximumsalt height prior to drainage is readily determined.

When the salt has accumulated to a level 37 such as shown in FIGURE 2,and the reduction of the PuCl3 is complete, stopper rod 39 is raised topermit the salt to discharge through cavities 40 and 41 and tube 42. Thedischarge of plutonium temporarily ceases, as the level in riser 33adjusts to a value lower than the maximum 36. No plutonium metal canfollow the outgoing salt, as the location of cavity 40 is higher thanthe maximum plutonium level 36, i.e., the intersection of riser 33 andcavity 27. There can be no pumping action to force ment, but thehorizontal salt drainage cavity because of the equal gas pressures abovesuch liquid and above'the plutonium in riser 33.

The above described salt drainage is, of course, accomplished veryquickly. stopper rod is lowered to the closing position, and theadditions of raw materials are recommenced. Although the salt dischargeis batchwise, the llowrof plutonium, the product for which the structurewas devised, is halted for only a few seconds out of every l minutes orso.

Thus the apparatus of FIGURE 2 provides a means for obtainingsubstantially a continuous reduction of the plutonium halide to themetal.

FIGURE 3 illustrates an apparatus similar in most respects to theembodiment of FIGURE 2, analogous parts being designated by the samenumerals preiixed by the digit fl to form a 100 series. Thus thetantalum block 121, through cavity 127, plutonium exit tube 128, inertgas inlet tube 129, frusto-conical cavity 131, vertical cavity 132,diagonal riser 133, liquid plutonium 134, salt melt 135, maximumplutonium level 136, horizontal cavity 140, salt drainage cavity 141,salt drainage tube 142 and salt-plutonium interface 144 .correspond tothe parts of FIGURE 2 numbered in the sub-one hundred series, as abovementioned, and are similarly disposed. The major differences are that inFIGURE 3 a smaller bore reaction chamber 145 and correspondingly smallerco-axial and sealingly registering furnace tube 146 are provided, saltaddition tube 147 is joined in sealing and registering relationship witha corresponding cavity 148 in tantalum block 121, such cavity 148 isconnected to the lower part of reaction chamber 145 by passage 149 (notnecessarily diagonal as shown), and the reducing metal is in the form ofa rod 150 suspended in the salt melt 135 by a supporting structure atthe top of furnace tube 146 (not shown). This structure may includesuitable means for lowering rod 150 into the melt as it is consumed.

There is no stopper rod in the FIGURE 3 embodi- 140 is disposed at ahigher location in reaction chamber 145, and the vertical salt drainagecavity 141 is correspondingly longer than the corresponding elements ofthe FIGURE 2 embodiment. Cross tubes 151 and 152 permit the iiow of theinert gas introduced through 129 into tubes 146 and 147 to equalize thepressures therein with the pressure exerted on the surface of theplutonium in riser 133. The long length of reducing metal rod 150immersed in salt melt 135 insures adequate surface for the reductionreaction. Element 153 is a tantalum plug, removable for drainagepurposes during shutdown.

While it is apparent that the FIGURE 3 embodiment may -be operated in amanner similar to that of the FIGURE 2 apparatus, i.e., adding the saltsas lgranules and melting them in the reaction chamber 145 and cavity148, the preferred method of operation is by the introduction of thesalt composition to be used as a liquid phase. Thus the liquid saltphase added through 147 is most conveniently the end product of theprocess disclosed in the patent issued to Reavi's et al., U.S. Pat.2,886,410.V That patent discloses a process by which a partially spentplutonium fuel displaces the Zinc in a chloride meltto form a melt ofPuCl3 and NaCl, at the same time stripping a number of fission productsfrom the plutonium by preferential dissolution and distillation. Sincethat process may be carried on continuously and since one of the overallobjectives of the present invention is the development of a continuousprocess for the purification (decontamination) of such plutonium fuels,the end product of that process is piped into the tube 147 as a liquid.Otherwise the operation of the FIGURE 3 embodiment is the same as theoperation of the FIGURE 2 embodiment, except that the rate of rise ofthe salt phase in reaction chamber 145 mus-t Immediately thereafter the-Vout any liquidY below the lower wall defining cavity 40 Vvbe morecarefully controlled to insure -a maximum reduction of the PuCl3 by thereductant rod 150.

yIn considering the minimum and optimum operating temperatures for thereductions exemplified above and illustrated as adaptable forsemi-continuous and continuous operation with the apparatus embodimentsof FIGURES 2 and 3, respectively, it is apparent that a number offactors must be considered. In each process the minimum temperature mustexceed the melting point of plutonium (640 C.) or its alloys, in thecerium or cerium-cobalt reductions, -to obtain a Well consolidated metalproduct, and must also exceed the melting points of both the reactantsalt and the product salt. These melting points, for Ithe pure undilutedsalts, are, in degrees Celsius:

FuCl3 l 770 CaCl2 772 LaCl3 870 CeCl3 810 When the PuCl3 is diluted withNaCl, the melting points of the reactant salt and the product salt arereduced. Each of the four systems discussed has a simple eutectic typeof phase diagram with no compound formation, the eutectic points beingapproximately:

Temperatures, Composition: degrees C.

77 w/o PuCl3-23 -w/-o NaCl 453 66 w/o LaCl3-34 w/o NaCl 543 67 w/oCaCl2-33 w/o NaCl 505 74 w/o CeCl3-26 w/o NaCl 500 (Pure NaCl melts atabout 800 C.)

In considering the alloys of plutonium formed by reductions with ceriumor cerium plus a cobalt diluent, reference to the above mentionedColfinberry patents indicates that the Pu-Ce alloys have a melting pointbelow 700 C. for a plutonium content ranging from 63 w/o to 100 w/o(S0-100 a/o), with a minimum melting point of about 600 C. at 95 a/oplutonium. (See U.S. Pat. 2,867,530.) The ternary alloys have meltingpoints below 500 C. for cobalt in the range 10-20 a/o, plutonium in anycontent up to 88 a/o, balance cerium as indicated in U.S. Pat.2,901,345.

Another factor to be considered is the material of the reaction Cruciblefor the particular reaction. As indicated in Examples 2, 3 and 5, it wasnecessary to raise the reaction temperature to about S25-850 C., inmaking calcium reductions in a ceramic crucible to obtain a well formedreduction button. No explanation for such required temperature increaseis apparent, and no necessity therefor appeared in the calciumreductions in a tantalum crucible or in the lanthanum reductions in aceramic Crucible. With the former, massive metal was produced at about800 C. from undiluted PuCl3 and at 700- 715 C. from the mixed salts ofapproximately eutectic composition (20 w/,o NaCl). The lanthanumreductions of salts of the same composition also yielded good metal atabout 700 C. No La reductions of undiluted PuCl3 were made because itwas desired to keep the reductant rod in the solid phase.

All of the PuCl3 reductions by cerium were carried on in ceramic (MgO-lOW/o TiO2) crucibles and resulted in well formed alloy buttons, rangingin cerium content from 1.1. to 27 w/o, with reaction temperatures in therange of from 650 to 710 C. The reductions of PuCl3 by Ce-Co alloys weremade in ceramic crucibles of the 13 C.), whichever is employed. For abatch process or for semi-continuous operation, the operatingtemperature may be high enough to permit melting of the reductant.

In considering optimum temperatures and time, it is apparent that littlewould be gained by increasing the reaction temperature for the calciumreductions above those indicated supra because the yields and thequality of the reduced metal are quite satisfactory The time at reactiontemperature poses no problem, as the attainment of a steady temperatureafter completion of a rapid exothermix excursion indicates completion ofthe reaction. With lanthanum and cerium reductions, no readily apparentexotherm occurs, and a comparision of Examples 6 and 7 with 8 and 9indicates an increase in yield with an increase in reaction time. It isalso possible that the yield may be increased by raising the temperatureof the reaction.

Examples 8 and 9 demonstrate a signiiicant decrease in the cerium toplutonium ratio in the lanthanum reductions. Thermodynamic calculationsindicate that :lanthanum will likewise reduce PuCl3 much more readily:than the chlorides of the other rare earths. Thermo- .dynamiccalculations also indicate that if conditions of the reduction arechanged so that a few percent of the PuCl3 remains in the salt aftercontact with the reductant,

' the concentration of rare earth contaminants in the metal product willbe lower than with complete reduction of the PuCl3. Thus it is indicatedthat at the expense of plutonium yield, greater decontamination fromrare earth impurities may be achieved. In the reduction with lanthanum,incomplete reduction may be achieved by shorter contact times betweenthe lanthanum and the salt or by limiting the amount of lanthanum addedto an amount insufficient to reduce all the PuCl3 present.

In the cerium reductions, the plutonium yield ranges from a minimum of90% to 93% as the cerium added to the salt is increased from thestoichiometric amount to a large excess, provided the temperature ismaintained at about 700 C., as indicated in Examples 10, 13 and 14. Acomparison of such examples with Example 12 indicates a higher yield at700 C. that at 650 C. The composition of the alloy may be predeterminedat the higher temperature by asuming a 90% yield and furnishing theindicated amount of cerium for the reduction plus an excess to dilutethe alloy as desired. Variations of temperature, size of charge,crucible material, etc., may improve the yield. If larger amounts ofsalt and reductant were to be used, the yield would probably be improvedand used as the basis of the necessary computation.

The plutonium yield in the PuCl3 reductions by cerium diluted withcobalt are somewhat higher, ranging upward from a minimum of 93%. Higherreaction temperatures seem to make little difference if the crucible andits contents are held at the lower melting temperature (550 C.) for areasonably long time. The composition of the alloy may be fairlyaccurately predicted by assuming a yield of 93% and adding theappropriate amount of cerium reductant, plus excess cerium and cobaltfor dilution as desired. If the conditions of the reduction are changedin such a way as to increase the plutonium yield, the new yield asdetermined for the changed conditions must be used in computing theamount of Ce-Co alloy to be used in the reduction.

In both types of cerium reduction, diluted and undiluted, Examples -18demonstrate appreciable decontamination from fission products such aslanthanum. Thermodynamic considerations based on the free energies offormation of the chlorides lead to the conclusion that the ceriumreductions leave behind in the slag certain other contaminationchlorides, eg., those of the alkali metals and the alkaline earthscalcium, strontium and barium. This conclusion is veried in the examplesabove with respect to NaCl, which remains unreduced as an inactiveconstituent of the salt phase.

What is claimed is:

l. A process for obtaining plutonium alloys and simultaneouslyseparating said plutonium from the rare earths other than cerium andlanthanum, the alkali metals, and the alkali earth metals which may beassociated with the source of said plutonium, comprising melting a saltphase containing plutonium trichloride and chlorides having negativefree energies of formation not less than that of plutonium trichlorideunder an inert gas blanket maintained during said process at not morethan about atmospheric pressure, contacting said salt phase with areductant selected from the class consisting of cerium and cerium-cobaltalloys, the composition and amount of said reductant being such as toprovide at least the stoichiometric amount of cerium for completereduction of said plutonium trichloride, heating the reactants asnecessary to a temperature of 550 C. to 775 C. the temperature beingmaintained until the reduction reaction reaches substantial equilibrium,and thereafter allowing said reactants and products to cool to roomtemperature.

2. The process of claim 1 in which said reductant is cerium and saidsalt phase consists essentially of plutoniurn trichloride and sodiumchloride in an approximately eutectic composition plus a minorpercentage of said other chlorides, the amount of said cerium addedbeing in a range from a minimum of the stoichiometric amount requiredfor the complete reduction of said plutonium trichloride to a maximum ofan excess to yield an alloy of plutonium and cerium containing suiicientplutonium for a nuclear reactor fuel.

3. The process of claim 2 in which said cerium range in said productalloy is from about 1.1 to about 27 weight percent and the temperatureis from about 650 C. to about 710 C.

4. The process Aof claim 1 in which said reductant is a cerium-cobaltalloy and said salt phase consists essentially of plutonium trichlorideand sodium chloride in an approximately eutectic composition plus aminor percentage of said other chlorides, the composition and amount ofsaid alloy relative to the amount of said salt being such that the alloyresulting from said process contains l0 to 20 atomic percent cobalt,plutonium in the range of from the minimum necessary for a nuclearreactor fuel to a maximum of 88 atomic percent, balance cerium, saidsalt and said reactant alloy being heated together in melting said salt.

5. The process of claim 4 in which said product alloy ranges from about5 weight percent cobalt, 30 weight percent plutonium and 65 weightpercent cerium to about 4 weight percent cobalt, 30 weight percentcerium and 66 percent plutonium, and the temperature is from about 550C. to about 775 C.

References Cited in the le of this patent UNITED STATES PATENTS2,948,586 Moore Aug. 9, 1960 OTHER REFERENCES Extractive and PhysicalMetallurgy of Plutonium and tl AllBloys, edited by Wilkinson. Article byAnselin, pp.

1. A PROCESS FOR OBTAINING PLUTONIUM ALLOYS AND SIMULTANEOUSLYSEPARATING SAID PLUTONIUM FROM THE RARE EARTHS OTHER THAN CERIUM ANDLANTHANUM, THE ALKALI METALS, AND THE ALKALI EARTH METALS WHICH MAY BEASSOCIATED WITH THE SOURCE OF SAID PLUTONIUM, COMPRISING MELTING A SALTPHASE CONTAINING PLUTONIUM TRICHLORIDE AND CHLORIDE HAV-